The original Bush-era tax act was intended to be temporary, as were all the various subsequent tax acts, leaving taxpayers with constant uncertainty about the future.

The American Taxpayer Relief Act of 2012 attempts to bring some permanence and certainty to the landscape. Now, with that said, please keep in mind that the government always has the ability to pass new laws.

Even though these new changes are considered "permanent" in the language of the act, Congress and the president could vote to change those laws if they deem it appropriate in two months, two years or two decades. Remember, prohibition was considered "permanent" when it was originally passed as well.

One of the temporary provisions from the 2010 tax act made permanent by the new law is portability. The new portability rules allow spouses to effectively share their estate tax exemptions. As a reminder, the 2012 tax act also maintained the unification of the federal estate, gift and generation-skipping transfer tax, and the exemption for 2013 is $5.25 million, with a top tax rate of 40 percent.

Portability allows a deceased spouse's estate to transfer the remaining unused exemption to the surviving spouse. The surviving spouse can then add the transferred exemption amount to his or her own exemption, thereby increasing the amount transferred to beneficiaries free of federal estate tax.

For example, if Tom dies in 2013 and has a taxable estate of $2.25 million, he has a remaining $3 million exemption. His estate can elect to transfer that remaining $3 million exemption to his wife, Mary. Assuming Mary has not used any of her exemption for gifting, she now has a total exemption of $8.25 million (Jane's $5.25 million, plus John's portable remaining $3 million).

If the surviving spouse is predeceased by more than one spouse, he or she is limited to the lesser of $5.25 million or the unused exemption amount of the last deceased spouse.

Portability is a great tool that can be used in estate planning. It means that a married couple can exclude more than $10 million from federal estate taxes without significant tax planning or the use of trusts. However, it's important to remember that in New York, estates of more than $1 million are subject to state estate tax, with a top rate of 16 percent.

So, now that we have a little more permanence in the estate-tax landscape, this is a great time to sit down with your financial planner and estate planning attorney to see how it might work best in your estate plan.

Laura Medigovich is a certified financial planner and vice president for M&T Bank's Hudson Valley region. The views expressed by the author are her own and are not endorsed by M&T Bank, M&T Securities or their affiliates.